Presently, the industrially used thermoplastic elastomers (hereinafter abbreviated as TPE) are roughly divided in two types: TPE comprising a block copolymer consisting of soft segments and hard segments and TPE comprising a partially crosslinked rubber called elastomer alloy and a plastic phase-separated therefrom. As the former type of TPE, there are known a block copolymer consisting of segments of an aliphatic polyether such as polytetramethylene glycol and segments of a polyester such as polyethylene terephthalate and polybutylene terephthalate, which is called polyester elastomer, and a block copolymer consisting of segments of aliphatic polyether and segments of a polyamide such as polydodecanolactum, which is called polyamide elastomer. As the latter type of TPE, there is known, for instance, an elastomer alloy yielded from dynamic vulcanization of an alloy of polypropylene and ethylene-propylene-diene terpolymer.
European Patent laid-Open Specification 0287233 discloses preparation of a polymer solution for coating by using a copolymer having an aromatic polyester in the side chain, namely a copolymer having an aromatic polyester covalently bonded to an acrylic or polyester resin, and it is claimed that this polymer solution is capable of forming a coating film with high hardness. This patent specification, however, is silent on thermoplastic resin and TPE.
The TPE's comprising the block copolymers consisting of soft and hard segments are the relatively hard elastomers which are over 40 in D scale of Shore hardness. Also, these TPE's are subject to large compression set and not so high in thermal resistance.
On the other hand, the elastomer alloys are capable of forming soft elastomers of down to about 30 in A scale of Shore hardness, but they are poor in thermal resistance.